Two reinforced embankments on soft soils: Experience after more than twenty years
Two projects of embankments on soft soils with high-strength basal woven geotextile reinforcement are described. Started in 1981 and 1986, respectively they belong to the first one's using preloading plus reinforcement for autobahns and highways in Germany. Projects, measurements and evaluation are shortly presented, including long term strain measurements and durability evaluation until 2009 (for 28 resp. 23 years). The present publication is a continua tion ofthe work done forthe same embankments in 1995 and published in 1998-1999. To our knowledge such a follow ing up for more than twenty years is quite rare and is believed to be very useful.
Two projects of embankments on soft subsoil with high-strength woven basal reinforcement have been started in Germany: "Rübke" in 1981 and "Grossenmeer" in 1986. "Rübke" is a pure test em bankment. "Grossenmeer" is an integral part of the federal highway B 211. High-modulus polyester woven is used with 200 kN/m and 400 kN/m UTS, respectively and < 10 % ultimate strain. Long term strength (durability) at "Rübke" and long term strains at "Grossenmeer" are being registered until now for 28 and 23 years, respectively. Summarizing some focal points:
Stability calculations according to DIN 4084 (Bishop) are correct enough, at least when high ten sile force at low short- and long-term strain is mobi lized to restrain deformations. The woven used proved to resist unforeseen overstressing. The rein forcement is still under tension after 23 years. Local weaker subsoil zones can easily result in reinforce ment overstressing and/or failure tendency; it should be kept in mind when selecting safety factors. The reduction of strength and tensile moduli due to aging (environmental effects) is ca. 1.5 % in 28 years for the high tenacity polyester woven used, i.e. ca. 0.5 % per 10 years.